It's the whole publicity thing and public reaction paired with the lack of knowledge about the matter.
First of all, there is a very good chance that you reach your twenties, or even more without knowing much about transgenders. Society just reached the point where the whole gay thing is pretty much established, and the acceptance (or, from some, tolerance) of it is becoming bigger and bigger. I imagine parents now have this talk with their children, while 20 years ago it was rather taboo. The topic of transgenders is probably not even in baby shoes in some ciuntries, so many people's initial reaction "what the fuck" or "he's just gay, right?". You can't expect much, when even heterosexuality is somewhat of a taboo topic in schools. Even in high-school sex eds we were taught nothing. Good luck to jumping to understand transgenders.
Then I'm sure there were responses - which could contest the usual crazed feminist reply quality - to some non-hurtful, but confused responses to the whole transformation, and when your confusion is met with some angry person trying to give you a lecture and acting like being transgender is as known as that the grass is green, and if you are not aware of it you are some uneducated pig, then it's easy to hate on the whole topic.
Also, the media did what the media does, and it's just repelling. She's not the first who had such an operation, I'm sure there were others who even suffered more, but you can't sell a random dude transforming into a random dudette. I guess, for transgenders, it's great to have a hero, and worths being whored out by the media. Everyday folks, though, worrying about their jobs, family, healthcare, whatever, might have different priorities.
I for one think, that it's just a beginning of some serious shitstorm going down along the next decades, when arguments will rise whether to call a transgender on their pre-op or post-op gender, what about those who can't afford it, should they get help from the state with the operations, and where should a transgender go to pee, or to play sports, or to.... Oh yeah, it will be nasty. I mean, homosexuality was a pretty straightforward thing, yet it's still in the process of being accepted, but some of the concerns about transgenders are not easy at all, and there are and will be good arguments and counter arguments for those.